Formula#installed_prefix: use PkgVersion
Formula#installed_prefix: use PkgVersion

Also check stable_prefix when current acitve_spec is not :stable

amar-laksh/brew_sudo,EricFromCanada/brew,mahori/brew,gregory-nisbet/brew,claui/brew,reitermarkus/brew,aw1621107/brew,DomT4/brew,vitorgalvao/brew,MikeMcQuaid/brew,mahori/brew,mgrimes/brew,gregory-nisbet/brew,sjackman/homebrew,toonetown/homebrew,zmwangx/brew,zmwangx/brew,sjackman/homebrew,nandub/brew,reitermarkus/brew,claui/brew,palxex/brew,tonyg/homebrew,JCount/brew,alyssais/brew,amar-laksh/brew_sudo,MikeMcQuaid/brew,mgrimes/brew,rwhogg/brew,DomT4/brew,muellermartin/dist,reitermarkus/brew,konqui/brew,EricFromCanada/brew,jmsundar/brew,reitermarkus/brew,bfontaine/brew,Linuxbrew/brew,hanxue/linuxbrew,EricFromCanada/brew,jmsundar/brew,nandub/brew,Linuxbrew/brew,konqui/brew,konqui/brew,AnastasiaSulyagina/brew,rwhogg/brew,vitorgalvao/brew,mistydemeo/homebrew,staticfloat/brew,maxim-belkin/brew,staticfloat/brew,claui/brew,vitorgalvao/brew,ilovezfs/brew,tonyg/homebrew,zmwangx/brew,nandub/brew,claui/brew,ilovezfs/brew,gregory-nisbet/brew,JCount/brew,ilovezfs/brew,hanxue/linuxbrew,gordonmcshane/homebrew,MikeMcQuaid/brew,aw1621107/brew,gordonmcshane/homebrew,sjackman/homebrew,pseudocody/brew,tonyg/homebrew,JCount/brew,mahori/brew,aw1621107/brew,DomT4/brew,MikeMcQuaid/brew,gordonmcshane/homebrew,AnastasiaSulyagina/brew,palxex/brew,EricFromCanada/brew,maxim-belkin/brew,rwhogg/brew,Homebrew/brew,pseudocody/brew,reelsense/brew,alyssais/brew,Homebrew/brew,vitorgalvao/brew,mgrimes/brew,mistydemeo/homebrew,hanxue/linuxbrew,nandub/brew,sjackman/homebrew,bfontaine/brew,staticfloat/brew,mistydemeo/homebrew,Homebrew/brew,JCount/brew,mahori/brew,muellermartin/dist,reelsense/brew,toonetown/homebrew,AnastasiaSulyagina/brew,pseudocody/brew,jmsundar/brew,Linuxbrew/brew,bfontaine/brew,maxim-belkin/brew,muellermartin/dist,palxex/brew,reelsense/brew,konqui/brew,DomT4/brew,Linuxbrew/brew,alyssais/brew,toonetown/homebrew,amar-laksh/brew_sudo,Homebrew/brew